Measurement of junction temperature of an AlGaAs/GaAs heterojunction bipolar transistor operating at large power densities

An electrical method to determine the junction temperature of a power bipolar transistor is presented. The success of this method does not rely on the constancy of thermal resistance over the wide range of operating temperatures. It is hence suitable for transistors operating at high power densities where conventional measurement techniques would not apply. Using this method, we establish that the junction temperature can be 40°C higher than the product of the low temperature thermal resistance and the power dissipation